1. Field of the Invention
The present invention relates to an internal combustion engine and particularly, to an internal combustion engine constructed, so that the temperature of an exhaust gas produced in a combustion chamber can be maintained at a high level.
2. Description of the Background Art
In a conventional internal combustion engine, a combustion chamber is provided in a cylinder head on one side of a partition wall, and a cooling water passage is provided in the cylinder head on the other side of the partition wall (for example, see Japanese Patent Application Laid-open No.10-212946).
In order to utilize an exhaust gas as a heat source in a Rankine cycle system and to promote the warming and achieve the early activation of an exhaust gas purification system and the like, it is desirable that the temperature of the exhaust gas produced in the combustion chamber be maintained at as much a high level as possible.
In the conventional example, however, the following problem is encountered: The entire combustion chamber is cooled in such a manner that the extent of cooling of the partition wall is matched to a region where the heat load is the largest. Therefore, a region where the heat load is smaller is cooled to an excessive extent, and the entire combustion chamber tends to be overcooled. As a result, the temperature of the exhaust gas is lower and hence, it is impossible to meet the above-described modes sufficiently.
It is an object of the present invention to provide an internal combustion engine of the above-described type, wherein the temperature of the exhaust gas can be maintained at a high level by maintaining the combustion chamber at a high temperature.
To achieve the above object, according to the present invention, there is provided an internal combustion engine comprising a combustion chamber provided in a cylinder head on one side of a partition wall, a heat-insulating layer provided in the cylinder head on the other side of the partition wall, and cooling passages provided in a plurality of regions provided with different heat loads in the partition wall, respectively, so that the flow rate of a cooling medium is decreased from the cooling passage existing in the region of the largest heat load to the cooling passage existing in the region of the smallest heat load.
With the above arrangement, the plurality of regions of the different heat loads in the partition wall can be cooled to a necessary and minimum extent depending on the magnitudes of the heat loads. In addition, it is possible to suppress the propagation of heat to a main body of the cylinder head leading to the partition wall by the heat-insulating layer, thereby maintaining the combustion chamber at a high temperature to maintain the temperature of an exhaust gas at a high level.
According to the present invention, there is also provided an internal combustion engine, wherein the occupation rate of the region of the smaller heat load in the partition wall and the occupation rate of the region of the heat load larger than that of such region in the partition wall are such that the former is larger than the latter; the sectional area of the cooling passage existing in the region of the smaller heat load and the sectional area of the cooling passage existing in the region of the heat load larger than that of such region are such that the former is smaller than the latter; and the surface area of the cooling passage existing in the region of the smaller heat load and the surface area of the cooling passage existing in the region of the heat load larger than that of such region are such that the former is larger than the latter.
With the above arrangement, the function of the region of the larger heat load can be maintained by cooling such region depending on the heat load. On the other hand, the wide regions can be cooled effectively and uniformly to a necessary and minimum extend by a small amount of the cooling medium, while enhancing the heat abatement, by a synergistic effect provided by permitting the flowing of the cooling medium at a higher speed in the region of the smaller heat load and by an enhancement in heat transfer coefficient attributable to an increase in passage surface area and an increase in Reynolds number.
According to the present invention, it is possible to provide an internal combustion engine, wherein the combustion chamber is maintained at a high temperature to maintain the temperature of an exhaust gas at a high level, whereby the internal combustion engine is suitable as a component for a heat source for a Rankine cycle, and it is possible to promote the warming and to achieve the early activation of an exhaust gas purification system.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.